The docents at Oak Grove Nature Center still have the letter, written by a little girl long since grown.

She might not have spelled well. But her message could not have been clearer:

"Thank you for giving us a towre (tour)," she wrote. "I never new there was such tings as hawks and wood pekers. I thawt they were made up."

It's now been more than 30 years since the first volunteers opened the doors of the center within Oak Grove Regional Park off Eight Mile Road.

And even today, a small but dedicated nucleus of volunteers keeps those doors open - even if most park visitors have no idea the center exists.

Why do they keep at it? That letter, for starters.

"To me, it's a birthright of all our children to know what exists in all of nature," said longtime volunteer Martha Mallery.

The size of the group has varied over the decades, as has the level of support from San Joaquin County, which operates the park. A staffer who coordinated the nature center the past several years was transferred last year to Micke Grove Zoo, and volunteers say their numbers have thinned to the point where they don't have enough people to host the annual BugFest celebration next month.

They do manage to keep the center open most weekends, to feed the snakes and frogs, and to take busloads of schoolchildren on walks through the native plant garden past the American Indian tule hut and the acorn-grinding stone. Now the volunteers are getting ready for what they hope will be a busy spring and summer season.

"I don't think the nature center would really even exist without the volunteers," said Duncan Jones, San Joaquin County's parks administrator. "It was started by the volunteers and it was kept going by them."

Sheldon Barr is the character in this group. With a thick new England accent and a thicker gopher snake wrapped around his wrist, he'll introduce you personally to the stuffed critters within the nature center's life-size diorama.

Perhaps exaggerating - though with Barr, it's hard to tell - he says that the children who visit barely know the difference between the replicas inside of the center and the real animals sometimes seen scurrying between the park's proud oak trees.

He wants to change that.

Like many of the volunteers, Barr has no formal training in plants or animals. Thirty years ago he brought his daughters to the park. They grew up, but he never stopped coming.

"I don't like change," Barr said.

Both of those daughters are pregnant and expect to give birth within days of each other this summer, Barr said.

"Now I'm going to be taking my grandchildren here," he said.

Darryl Pedro grew up on a dairy, where he learned to appreciate working outdoors.

Now a retired glass manufacturer, he considers volunteering at the nature center to be a form of community service.

"We've got a beautiful city here, and we want everyone to know about it," said Pedro, 71.

He finds that beauty even in tiny sprigs of miner's lettuce, an edible native plant he somehow spotted last week while walking through the park's expansive grasses.

"Here we go, here we go!" he said upon that discovery.

No one else would have seen the difference.

"Every time you come out here it makes you feel better," he said.

As a girl, Martha Mallery went on family pack trips into the Sierra Nevada. When she was 4 years old, she climbed Mount Whitney, the highest peak in the lower 48 states (though she admits she must have been carried most of the way).

"It was my mother who was really interested in wildflowers at the time," she said. "It was something I think was imprinted on me."

Decades later, Mallery - a member of the California Native Plant Society - has labored many hours on the gardens around the nature center, assisted by other volunteers and, occasionally, by students from San Joaquin Delta College.

It is Mallery who remembers most vividly that letter received from the little girl so many years ago.

And she remembers her reaction when she read it.

"I thought, 'Gee, we'd better be here,'" she said. "'We'd better show people what nature is like.'"